JPH09276245A - Rf coil for mri, and mri device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sufficiently large arresting impedance without causing a loss in switching by providing an inductor so as to constitute a parallel resonance circuit with a first capacitor, and connecting the first and second capacitors in series by a switching means. SOLUTION: An inductor L0 equivalently represents the inductor generated in the element of a receiving coil 50, and a capacitor C0 constitutes a resonance circuit with the inductor L0 and has a capacity synchronized to the Larmor frequency. A blocking circuit 62 performs the effective/invalid switching of operation of the receiving coil 50, and a bias circuit 65 supplies a bias, whereby the effective/invalid switching is performed. The blocking circuit 62 has a synchronizing capacitor (composed capacity C0) formed of capacitors C1', C2' connected in series, and takes out a received signal from both ends of the capacitor C2'. The continuity/non-continuity of diodes D1, D2 is controlled by the bias from the bias circuit 61.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MRI RF coil used in a magnetic resonance imaging (MRI) apparatus and an MRI apparatus, and more particularly,
The present invention relates to an MRI RF coil having a valid / invalid switching circuit that switches valid / invalid of an operation of the MRI RF coil during transmission / reception, and an MRI apparatus using the MRI RF coil having a valid / invalid switching circuit.

[0002]

2. Description of the Related Art An MRI apparatus uses a nuclear magnetic resonance phenomenon to measure a nuclear spin density distribution, a relaxation time distribution, and the like at a desired inspection site in a subject, and uses the measured data to determine a cross section of the subject. An image is displayed.

A nuclear spin of a subject placed in a uniform and strong static magnetic field generator precesses around a direction of the static magnetic field at a frequency (Larmor frequency) determined by the strength of the static magnetic field. Therefore, when a high-frequency pulse having a frequency equal to the Larmor frequency is irradiated from the outside, spins are excited and transit to a high energy state.

This is called a nuclear magnetic resonance phenomenon. When the irradiation of the high frequency pulse is terminated, the spin returns to the original low energy state with a time constant corresponding to each state, and at this time, the electromagnetic wave is irradiated to the outside. This is detected by a high frequency receiving coil (RF coil for MRI) tuned to the frequency.

At this time, a triaxial gradient magnetic field is applied to the static magnetic field space for the purpose of adding position information to the space. As a result, position information in space can be captured as frequency information.

In such an MRI apparatus, an MRI RF coil used for applying a high-frequency rotating magnetic field to a subject or for receiving an electromagnetic wave generated by the subject accommodates the subject therein, A high-frequency current is applied to the part of the wire (element) around the subject.

As such an MRI RF coil,
There are a transmission / reception coil used for both transmission and reception, a transmission dedicated coil used only for transmission, and a reception dedicated coil used only for reception.

In the case of this transmission-dedicated coil, the transmission-dedicated coil does not operate in order to prevent the pulse of the Larmor frequency from the subject from being absorbed by the transmission-dedicated coil after the transmission (irradiation of the high-frequency pulse) is completed. Need to switch to.

Similarly, in the case of the receiving-only coil, the receiving-only coil is switched so that it does not directly receive the high-frequency pulse from the transmitting-only coil during transmission (irradiation of the high-frequency pulse). There is a need.

For the above switching, the coil element is provided with an effective / ineffective switching circuit. FIG. 11 is a configuration diagram showing an example of a detailed configuration of the blocking circuit 60 as such an effective / ineffective switching circuit. Here, the case where the blocking circuit 60 is composed of the diode D is shown.

In such a circuit configuration, the MRI R
The inductor L0 of the element of the F coil and the capacitance of the capacitor C0 are adjusted so as to tune to the Larmor frequency. In practice, the inductance component is determined by the shape of the element, etc., and thus the capacitance of the capacitor C0 is also determined.

In the case of the receiving coil 50 having the structure shown in FIG. 11, when the receiving coil 50 receives, a forward bias current is applied to the diode D from the bias circuit 61 to bring the diode D into a conducting state.

As a result, the effect of the diode D is apparently eliminated and only the components of C0 and L0 are present, and the receiving coil 50 is in a state of being tuned to the Larmor frequency. on the other hand,
At the time of transmission of the transmission coil 40, the forward bias current to the diode D is stopped (or the reverse bias is applied) to bring the diode D into a non-conducting state.

As a result, the loop of the element of the receiving coil 50 is apparently cut, and the MRI RF coil does not operate. In the above case, the conduction resistance of the diode D (the resistance when the forward bias is applied) is not completely zero at the time of reception by the reception coil 50, and a loss occurs due to a minute resistance value. To do.

Further, in order to prevent the operation as a coil, it is necessary to apply a large reverse bias voltage to the diode, and there is a problem that the switching control of the diode is troublesome.

In view of the above problems, a blocking circuit as shown in FIG. 12 may be used. This figure 1
In the second circuit, a series connection circuit of an inductor L1 for blocking tuning and a diode D is arranged in parallel with the capacitor C0. Then, the reception signal is taken out from both ends of the diode D.

In this case, the conduction / non-conduction state of the diode D is controlled in a state opposite to that of the case shown in FIG. That is, when the transmission coil 40 transmits, the diode D
Is controlled to a conductive state so that L1 and C0 resonate in parallel.

As a result, the element of the receiving coil 50 is cut off, and the transmitted high frequency pulse is not excited in the receiving coil 50. Further, in this state, since the diode D is turned on only for parallel resonance, problems of loss and heat generation do not occur.

Since the diode D is made non-conductive at the time of reception by the receiving coil 50, the problem of loss with respect to the received signal does not occur. By the way, this receiving amplifier 7
In order to make the noise figure of 0 (hereinafter referred to as NF) the optimum value, the impedance of the receiving coil 50 when viewed from the feeding point is 50 ohms when the MRI apparatus is used (when the subject is mounted in the coil). Is preferred. But,
Actually, it is often about several kilo Ω due to the capacity of the capacitor C0.

Therefore, as shown in FIG. 13, the capacitor C0 on the feeding point side is divided into a small capacitance C1 and a large capacitance C2, and the combined capacitance of C1 and C2 is set to be equal to C0. deep. This circuit configuration is called a C division type blocking circuit in this specification.

By doing so, the impedance of the feeding point can be lowered due to the influence of the large-capacity capacitor C2, the input impedance of the receiving amplifier 70 can be matched, and NF can be optimized. You will be able to.

[0022]

By the way, since the intensity of the static magnetic field and the Larmor frequency are in a proportional relationship, the Larmor frequency also decreases in the low magnetic field type MRI apparatus having a small static magnetic field. In this case, if the size of the RF coil for MRI is constant, the inductor portion L0 is constant, so that the capacitance of the capacitor C0 becomes large in order to tune to the Larmor frequency.

Therefore, when the capacitor C0 is divided into C1 and C2, the capacitance of the capacitor C2 is low magnetic field MRI.
The device is even larger. As a result, in the blocking circuit 60, the value of the inductor L1 becomes small, and the blocking impedance at the time of resonance becomes a problem.

That is, when the capacitance C0 of the capacitor becomes large, there arises a problem that the impedance ZB (ZB = L / (CR), this ZB is called a blocking impedance) in the tuned state of the parallel resonant circuit does not become sufficiently large.

As a result, at the time of transmission, the receiving coil 5
Since the current flowing through each component of 0 becomes large, the thermal load of each component becomes large. Further, similar to the above-mentioned problem in the receiving coil, the same problem occurs in the transmitting coil, and it has been desired to solve the problem.

The present invention has been made in view of the above points, and a first object thereof is effective / ineffective in obtaining a sufficiently large blocking impedance without causing a problem such as loss in switching. It is to realize an RF coil for MRI that includes a switching circuit and also considers impedance matching.

The present invention has been made in view of the above points, and a second object thereof is effective / ineffective in obtaining a sufficiently large blocking impedance without causing a problem such as loss in switching. It is to realize an MRI apparatus including a switching circuit and considering impedance matching.

[0028]

Means for Solving the Problems The inventor of the present application has made earnest researches to improve the problems relating to the effective / ineffective switching circuit at the time of transmitting and receiving the conventional RF coil for MRI, and as a result,
The present invention has been completed by newly finding an optimal arrangement of each element that makes it possible to achieve both impedance matching and blocking impedance of the receiving system.

That is, the present invention, which is means for solving the problems, is basically as described in the following (1) to (7). (1) According to a first aspect of the invention, a tuning capacitor in which first and second capacitors are connected in series, an inductor provided so as to form a parallel resonant circuit with the first capacitor, and in the conductive state, A valid / invalid switching circuit at the time of transmission / reception, which comprises a parallel resonance circuit composed of a first capacitor and the inductor, and switching means for connecting the first and second capacitors in series in an element in a non-conductive state. Is provided in the element, and a signal is input or output from both ends of the second capacitor, which is an RF coil for MRI.

In the MRI RF coil according to the first aspect of the invention, when the switching element is in the conducting state, the first capacitor and the inductor form a parallel resonance circuit, and the parallel resonance state results in high impedance. MR
The operation as the I RF coil is stopped.

In this case, the switching element is in the conducting state, but the resonance circuit is in the parallel resonance state and the RF for MRI.
Block the current through the coil. Moreover, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding unit, it becomes possible to obtain a sufficiently large blocking impedance.

When the switching element is in the non-conducting state, the series connection circuit of the first capacitor and the second capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonant circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting the received signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding portion can be maintained at an appropriate value. In this case, the switching element is in the non-conducting state and the MR
Since it has nothing to do with the current flowing through the I RF coil, the loss of the switching element does not affect the operation.

(2) According to a second aspect of the present invention, a parallel resonance circuit is formed with a tuning capacitor in which first and second capacitors are connected in series and the first capacitor via a first switching means. An effective / ineffective switching circuit at the time of transmission / reception, which includes an inductor provided in the second switching unit, and a second switching unit connected in series with the first switching unit and arranged in parallel with the second capacitor. MR is provided in the element to input or output a signal from both ends of the second capacitor.
It is an RF coil for I.

In the MRI RF coil according to the second aspect of the invention, when the first switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance. Therefore, the operation as the RF coil for MRI is stopped.

In this case, the first switching element is in the conducting state, but the resonance circuit is in the parallel resonance state and the MRI is performed.
The current flowing through the RF coil for use is blocked. Therefore, the first
The conduction resistance of the switching element is not a loss of the RF coil for MRI.

Further, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding portion, it becomes possible to obtain a sufficiently large blocking impedance. Further, since the second switching elements on both ends of the second capacitor are in the conductive state, an unnecessary signal is not supplied or output.

When the switching element is off, the series connection circuit of the first capacitor and the second capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonant circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting a reception signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding portion can be maintained at an appropriate value. In this case, the switching element is in the non-conducting state and the MR
Since it has nothing to do with the current flowing through the I RF coil, the loss of the switching element does not affect the operation.

(3) A third aspect of the present invention is the first aspect of serial connection.
Tuning capacitor composed of a capacitor and a second capacitor, first switching means having one end connected to a connection point of the first capacitor and the second capacitor, and one end of the capacitor in the capacitor. An inductor connected to one end of the first capacitor side, the other end of which is connected to the other end of the first switching means, and which has parallel resonance with the first capacitor at the frequency of the high frequency magnetic field, and one end of which is the tuning capacitor. Second switching means connected to the other end of the first switching means and the other end of the second switching means connected to the connection point between the first switching means and the inductor, and turned on / off together with the first switching means. The element is provided with a valid / invalid switching circuit for transmission / reception, and a signal is input or output from both ends of the second capacitor. R for MRI, which comprises carrying out the
It is an F coil.

In the MRI RF coil according to the third aspect of the present invention, when the first switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance. Therefore, the operation as the RF coil for MRI is stopped.

In this case, the first switching element is in the conducting state, but the resonance circuit is in the parallel resonance state and the MRI is performed.
The current flowing through the RF coil for use is blocked. Therefore, the first
The conduction resistance of the switching element is not a loss of the RF coil for MRI.

Further, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding portion, it becomes possible to obtain a sufficiently large blocking impedance. Further, since the second switching elements on both ends of the second capacitor are in the conductive state, an unnecessary signal is not supplied or output.

When the switching element is off, the series connection circuit of the first capacitor and the second capacitor acts as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonance circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting a reception signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding section can be maintained at an appropriate value. In this case, the switching element is in the non-conducting state and the MR
Since it has nothing to do with the current flowing through the I RF coil, the loss of the switching element does not affect the operation.

(4) A fourth invention is a tuning capacitor in which first to third capacitors are connected in series, and the first invention.
And the inductor provided so as to form a parallel resonance circuit with the capacitor, and the first capacitor and the inductor in the conductive state form a parallel resonance circuit, and in the non-conductive state, the first to third capacitors are connected. The element is provided with an effective / ineffective switching circuit at the time of transmission / reception, which comprises a switching means connected in series in the element, and a combined capacitance of the first capacitor and the second capacitor is provided as the tuning capacitor. An RF coil for MRI, which is configured to have a capacitance equal to that of a third capacitor, and which inputs or outputs a signal from both ends of the second capacitor.

In the MRI RF coil according to the fourth aspect of the present invention, when the switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance. MR
The operation as the I RF coil is stopped.

In this case, the switching element is in the conducting state, but the resonance circuit is in the parallel resonance state and the RF for MRI.
Block the current through the coil. Moreover, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding unit, it becomes possible to obtain a sufficiently large blocking impedance.

When the switching element is in the non-conducting state, the series connection circuit of the first capacitor to the third capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonant circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting the received signal. You can choose such a large value.

With this structure, the blocking impedance can be increased and the impedance of the power feeding section can be maintained at an appropriate value. In this case, the switching element is in the non-conducting state and the MR
Since it has nothing to do with the current flowing through the I RF coil, the loss of the switching element does not affect the operation.

By providing the third capacitor C3 and maintaining the capacities of the first capacitor to the third capacitor in a predetermined relationship, it is possible to minimize the potential with respect to the GND on the coil and thus the stray capacitance. The current flowing through the object through the through-hole is also minimized, and the loss of the coil and the heat generation of the object are also minimized.

It should be noted that it is possible to provide an inductor forming a parallel resonance circuit with the third capacitor and a switching element for operating the parallel resonance circuit, and it is possible to realize a larger blocking impedance. .

(5) According to a fifth aspect of the invention, there is provided a tuning capacitor in which first to third capacitors are connected in series, and the first capacitor.
And the inductor provided so as to form a parallel resonance circuit with the capacitor, and the first capacitor and the inductor in the conductive state form a parallel resonance circuit, and in the non-conductive state, the first to third capacitors are connected. The element is provided with an effective / ineffective switching circuit at the time of transmission / reception, which comprises a switching means connected in series in the element, and a combined capacitance of the second capacitor and the third capacitor is provided as the tuning capacitor. An MRI RF coil configured to have a capacitance equal to that of one capacitor, and inputting or outputting a signal from both ends of the second capacitor.

In the MRI RF coil according to the fifth aspect of the present invention, when the switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance. MR
The operation as the I RF coil is stopped.

In this case, the switching element is in the conducting state, but the resonance circuit is in the parallel resonance state, and the RF for MRI is used.
Block the current through the coil. Moreover, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding unit, it becomes possible to obtain a sufficiently large blocking impedance.

When the switching element is in the non-conducting state, the series connection circuit of the first capacitor to the third capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonance circuit has a small value, and the second capacitor forming the power supply section has an impedance suitable for outputting a reception signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding section can be maintained at an appropriate value. In this case, the switching element is in the non-conducting state and the MR
Since it has nothing to do with the current flowing through the I RF coil, the loss of the switching element does not affect the operation.

By providing the third capacitor C3 and maintaining the capacities of the first capacitor to the third capacitor in a predetermined relationship, it is possible to minimize the potential with respect to the GND on the coil and thus the stray capacitance. The current flowing through the object through the through-hole is also minimized, and the loss of the coil and the heat generation of the object are also minimized.

It is also possible to provide an inductor forming a parallel resonance circuit with the third capacitor and a switching element for operating this parallel resonance circuit, and to realize a larger blocking impedance. .

(6) MR shown in (1) to (5) above
It is preferable that the switching means in the RF coil for I is a PIN diode because the high frequency impedance is high at the time of reverse bias, the forward resistance is low at the time of forward bias, and the resistance becomes pure resistance at high frequency.

(7) A seventh aspect of the invention is an MRI RF coil having an effective / ineffective switching circuit for switching effective / ineffective during transmission / reception in an element, and switching control for switching the operation of the effective / ineffective switching circuit. And a tuning capacitor in which a first capacitor for a parallel resonant circuit and a second capacitor for a power feeding unit are connected in series, the valid / invalid switching circuit comprising: And the inductor provided so as to form a parallel resonance circuit with the capacitor, and the first capacitor and the inductor form a parallel resonance circuit in a conductive state, and the first and second capacitors form a parallel resonance circuit in a non-conductive state. An MRI apparatus comprising a switching means connected in series in an element.

In the MRI apparatus according to the seventh aspect of the invention, when the switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance. The operation as the RF coil is stopped.

In this case, the switching element is in the conducting state, but the resonance circuit is in the parallel resonance state, and the RF for MRI is used.
Block the current through the coil. Moreover, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding unit, it becomes possible to obtain a sufficiently large blocking impedance.

When the switching element is off, the series connection circuit of the first capacitor and the second capacitor acts as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonant circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting the received signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding portion can be maintained at an appropriate value. In this case, the switching element is in the non-conducting state and the MR
Since it has nothing to do with the current flowing through the I RF coil, the loss of the switching element does not affect the operation.

Since the switching means in the above MRI RF coil is a PIN diode, the high frequency impedance is high at the time of reverse bias, the forward resistance is low at the time of forward bias, and it becomes a pure resistance in terms of high frequency. ,preferable.

Further, as capacitors connected in series,
As in (4) and (5) above, it is possible to use the first to third capacitors, and good results can be obtained as an MRI apparatus.

(8) R for MRI of (1) to (6) above
R for MRI used in F coil and MRI device of (7)
The F coil can be used in each of the case where only the transmission coil, the reception coil, and the transmission / reception coil perform transmission, and in the case where the transmission / reception coil only performs reception.

[0075]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the M of the present invention.
It is a block diagram which shows the receiving coil as an RF coil for RI, and the principle structure of an MRI apparatus.

<Embodiment> Here, an MRI RF coil having a receiving coil with a blocking circuit as an effective / ineffective switching circuit, and such an MRI RF coil
Description will be given taking the configuration of an MRI apparatus using a coil as an example. The same parts as those already described are designated by the same reference numerals.

In FIG. 1, the inductor L0 is an equivalent representation of an inductor generated by the element of the receiving coil 50, and C0 is a capacitor having a capacitance for forming a resonance circuit together with the inductor L0 and tuning for the Larmor frequency. Is.

The blocking circuit 62 is provided with a power supply section for switching the operation of the receiving coil 50 between valid and invalid and outputting a reception signal. Then, the bias circuit 61 as the switching control means (switching control circuit) supplies a bias to realize the valid / invalid switching.

After the reception signal from the blocking circuit 62 is amplified by the reception amplifier 70, various reception processes are executed by the reception circuit. The blocking circuit 62 includes a first capacitor C1 'and a second capacitor C2' which are connected in series.
And a tuning capacitor (combined capacitance C0) composed of The second capacitor C2 'is connected so as to extract the received signal from both ends.

The first capacitor C1 'and the second capacitor C2' have a first end connected to a connection point.
A diode D1 as a switching means of the first capacitor C1 'and one end thereof is connected to one end of the first capacitor C1' on the element side, and the other end thereof is connected to the other end of the diode D1. Has an inductor L1 '.

Further, one end is connected to the element side of the first capacitor C2 ', the other end is connected to the connection point between the diode D1 and the inductor L1', and is arranged so as to turn on / off together with the diode D1. The diode D2 is provided as a switching device for the second.

The conduction / non-conduction of the diodes D1 and D2 is controlled by the bias current or bias voltage from the bias circuit 61.

That is, the bias circuit 61 is connected to both ends of the switching means, and the bias circuit 61 receives an instruction from the CPU 10 regarding the timing of transmission / reception.

The bias circuit 61 controls conduction / non-conduction of the diode D1 and the diode D2 forming the switching means in accordance with transmission / reception of the MRI apparatus.

Here, it is desirable to use a PIN diode because it has a high-frequency impedance when reverse biased, a low forward resistance when forward-biased, and a pure resistance even at high frequencies.

Regarding the first switching means and the second switching means, the diode D shown here is used.
Various configurations other than 1 and the diode D2 can be used.

For example, it is possible to use various switches in addition to semiconductor switches such as transistors, FETs and thyristors. Further, as the bias circuit 61, various circuits (trigger pulse generation circuit etc.) capable of controlling conduction / non-conduction in a state suitable for various switching means can be used.

Although the first switching means and the second switching means are controlled by a common bias current here, the first switching means and the second switching means are separately provided. A configuration in which switching control is performed may be used.

In such a circuit configuration, the first capacitor C1 'is preferably set to a small value so as to have a sufficient blocking impedance when a parallel resonant circuit is constructed with the inductor L1'. .

Further, it is preferable to select a large value for the second capacitor C2 'constituting the power feeding section so that the impedance is suitable for outputting the reception signal. <During Transmission> FIG. 2 is a circuit diagram showing an equivalent circuit when the diodes D1 and D2 in the receiving coil 50 shown in FIG. 1 are in a conductive state due to the forward bias from the bias circuit 61 (during transmission).

In this case, the parallel conduction circuit of the first capacitor C1 'and the inductor L1' is formed by the conduction of the diode D1. Therefore, this parallel resonance circuit becomes a resonance state and blocks the current flowing through the receiving coil 50.

As a result, the receiving coil 50 is disabled during transmission. In this case, the first capacitor C1 'is
Since the capacitance can be selected without being affected by the impedance required for the power feeding unit, it is possible to obtain a sufficiently large blocking impedance.

Since the receiving coil 50 is not operating in this state, the conduction resistance of the diodes D1 and D2 forming the switching element does not cause the loss of the receiving coil 50.

When the switching element is in a non-conducting state at the time of reception, the series connection circuit of the first capacitor and the second capacitor works as a tuning capacitor.
Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonant circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting the received signal. You can choose such a large value.

With this structure, the blocking impedance can be increased and the impedance of the power feeding portion can be maintained at an appropriate value. The second capacitor C2 'is short-circuited by the diodes D1 and D2. Therefore, in addition to the disconnection of the element by the parallel resonant circuit described above, the input of the reception amplifier 70 is short-circuited, and thus it is possible to prevent a large voltage induced during transmission from being applied to the reception system.

<Receiving> FIG. 3 shows an equivalent circuit in the receiving coil 50 shown in FIG. 1 when the diode D1 and the diode D2 are non-conducting by the reverse bias from the bias circuit 61 (during receiving operation). It is a circuit diagram.

In this case, the first capacitor C1 'and the second capacitor C2' form a series circuit by non-conducting the diodes D1 and D2. Therefore, the combined capacitor of this series circuit becomes resonant with the inductor L0 at the Larmor frequency to perform the receiving operation. As a result, the receiving coil 50 becomes valid during reception.

Since the first capacitor C1 'and the second capacitor C2' are connected in series, the combined capacitance approaches the small value of the small first capacitor C1 'as described above.

Therefore, the second capacitor C2 'sets the impedance required for the power feeding portion to an appropriate value (for example,
It becomes possible to select a large capacitance for making it 50 Ω).

In this state, the receiving coil 50 is in the operating state, but the diodes D1 and D2 forming the switching element are in the non-conducting state, and the conduction resistance of the switching element does not cause a loss during reception. .

Further, in this case, since the switching element is in the non-conducting state and is not related to the current flowing through the RF coil for MRI, the loss of the switching element does not affect the operation.

<Effects Obtained by the Embodiments> As described in detail above, according to the above-described embodiments, the following effects can be obtained.

If the combined capacitance of the capacitors connected in series has a value suitable for the tuning capacitor, the capacitances of the first capacitor C1 'and the second capacitor C2' can be freely selected.

Therefore, the first capacitor forming the parallel resonance circuit as the blocking circuit has a small value, and the second capacitor C2 'forming the power feeding section has an impedance suitable for outputting the reception signal. You can choose a large value.

With such a configuration, it is possible to increase the blocking impedance and to keep the impedance of the power feeding portion at a low value, which is impossible in the past, at the same time. Become.

That is, this state will be described with reference to FIG. 4. Compared with the conventional C-division type shown in FIG. 13, the output impedance Zc is the same in that the impedance can be made low (50Ω or the like), but a blocking circuit is used. Sufficient blocking impedance Z that can be composed of small capacity C1 '
A great effect is obtained in that B'is obtained.

When the receiving coil 50 is disabled, the diode D
Since 1 and D2 are in the conducting state and the diodes D1 and D2 are in the non-conducting state when the receiving coil 50 is valid, the diodes D1 and D2 are irrelevant to the current (reception signal) flowing through the MRI RF coil during reception. Therefore, the conduction resistances of the diodes D1 and D2 do not affect the operation of the receiving coil 50.

Therefore, for MRI in which an effective / ineffective switching circuit capable of obtaining a sufficiently large blocking impedance without causing a problem such as loss at the time of switching is provided and also considering impedance matching with a receiving system. An RF coil can be realized.

Further, an MRI apparatus provided with an effective / ineffective switching circuit capable of obtaining a sufficiently large blocking impedance without causing a problem such as loss upon switching, and also considering impedance matching with a receiving system. Can be realized.

<Embodiment> In the above-mentioned embodiments, the valid / invalid switching at the time of switching the transmission / reception in the receiving coil has been described as an example, but it can also be used in the following. is there.

Effective / ineffective switching at the time of transmission / reception switching in the transmission coil: In this case, as shown in FIG. 5, a blocking circuit 6 as an effective / ineffective switching circuit at the time of transmission.
4 is enabled by the bias circuit 63 (diode D1
And D2 are controlled to be non-conductive, and the blocking circuit 64 is disabled (diode D1) during reception.
And D2 are conductive.

By doing so, impedance matching can be achieved between the transmitting circuit (power amplifier 30) having an impedance of 50Ω and the transmitting coil 40, and the transmitting power can be effectively used.

At the same time, a sufficiently high blocking impedance can be obtained at the time of reception, and a weak received signal will not be excited on the transmitting coil 40 side. Furthermore, since the diode D2 in parallel with the capacitor C2 'of the power feeding section is conducting at the time of reception, it is possible to reliably prevent unnecessary high frequency radiation from the transmission system.

The same operation can be performed when either transmission or reception is performed by the transmission / reception coil, and both impedance matching and blocking impedance can be achieved.

In this case, when the transmission / reception coil is used as the reception coil, the same operation as that of the above-mentioned reception-only RF coil for MRI may be performed. When the transmission / reception coil is used as the transmission coil, the above-mentioned transmission-only MR is used.
The same operation as that of the RF coil for I may be performed.

<Example of Embodiment> FIG. 6 is a block diagram showing the overall structure of an MRI apparatus having an effective / ineffective switching circuit as an example of the embodiment. Here, a configuration in which the receiving coil is provided with a blocking circuit as an effective / ineffective switching circuit will be described as an example.

The CPU 10 centrally controls the operation of the entire MRI apparatus, and controls transmission / reception and effective / ineffective switching. The transmission circuit 20 generates a high frequency pulse required for MRI, and the high frequency pulse is generated by the power amplifier 30.
It is amplified by and is supplied to the transmission coil 40.

At the time of reception, after the signal detected by the receiving coil 50 is amplified by the receiving amplifier 70, various receiving processes are executed by the receiving circuit 80. Then, the CPU 10 displays an image of the reception processing result on the display 90.

A blocking circuit 62 is provided so that the reception-only coil 50 does not receive the high frequency pulse being transmitted. The blocking circuit 62 is the CPU 10
A bias circuit 61 controlled by means of the above-mentioned step switches between valid / invalid.

That is, a blocking circuit 62 is arranged in the element of the receiving coil 50 in order to stop the operation of the receiving coil 50 by electrically disconnecting the loop.

Here, the MRI apparatus has been shown in which the receiving coil 50 performs the valid / invalid switching, but it is also possible to perform the similar valid / invalid switching in the transmitting / receiving coil and the transmitting coil.

<Example of Embodiment> FIG. 7 is a block diagram showing the principle structure of an MRI RF coil (reception coil) and an MRI apparatus as an example of the present invention.

Here, an MRI RF coil provided with a blocking circuit as a valid / ineffective switching circuit in the receiving coil, and an MR using such an MRI RF coil.
The configuration of the I device will be described as an example. The same parts as those already described are designated by the same reference numerals.

In the circuit shown in FIG. 7, the blocking circuit 62 includes the first capacitor C1 connected in series.
', A second capacitor C2' and a third capacitor C3
Tuning capacitor composed of and (combined capacitance C0)
It has. The second capacitor C2 'is connected so as to extract the received signal from both ends.

That is, the embodiment described above (FIG. 1).
It is characterized in that a third capacitor C3 is added to the above. Therefore, inductor L1 'and diode D
1 and D2 have the same configuration.

In such a circuit configuration, the first capacitor C1 'is preferably set to a small value so as to have a sufficient blocking impedance when the inductor L1' and the parallel resonance circuit are constructed. . Further, it is preferable to select a large value for the second capacitor C2 'constituting the power feeding section so that the impedance is suitable for outputting the received signal.

The capacitance ratios of the first capacitor C1 ', the second capacitor C2' and the third capacitor C3 are preferably set so as to satisfy the conditions described below.

If there is a portion having a high potential with respect to GND on the coil, a current will flow from the coil to the subject through the stray capacitance with the subject (which is considered to be approximately the GND potential). This current causes loss of the coil and heat generation of the subject. Therefore, it is preferable to minimize the current on the coil so that the potential with respect to GND is as low as possible.

As shown in the above embodiments, in the case where the capacitance is concentrated in two places, near the power feeding part and near the opposite position, the potential to GND is minimized. It suffices to realize the two points of equalizing the capacitances at the two locations so that the potentials at both ends of the capacitor at one location have the same magnitude and opposite signs.

In order to satisfy such a relationship, a third capacitor C3 is provided next to the second capacitor C2 '(on the side opposite to the first capacitor C1') in the power feeding section, and
Make sure to satisfy equations (1) and (2). C3 = 2C0 (1) 1 / ((1 / C1 ') + (1 / C2')) = 2C0 (2) The above equation is for the second capacitor C2 'and the third capacitor C3. This is a case where the jacket side (GND potential) of the coaxial cable that feeds power to the connection point is connected. When the jacket side (GND) of the coaxial cable is connected to the connection point between the first capacitor C1 'and the second capacitor C2', the following equations (1) 'and (2)' are used. Try to meet. C1 = 2C0 ... (1) '1 / ((1 / C2') + (1 / C3)) = 2C0 ... (2) 'Thus, the above conditions and are satisfied, and
The potential will be minimized. Therefore, the current flowing through the stray capacitance to the subject can be minimized, and the loss of the coil and the heat generation of the subject can be minimized.

If the range satisfies the above expression (2), C
Since the ratio of the capacitances of 1'and C2 'can be freely selected, it is possible to select a value suitable for the above-mentioned blocking impedance and matching with the transmission / reception circuit.

<During Transmission> FIG. 8 is a circuit diagram showing an equivalent circuit when the diodes D1 and D2 in the receiving coil 50 shown in FIG. 7 are in a conducting state due to the forward bias from the bias circuit 61 (during transmission). Is.

In this case, the parallel conduction circuit of the first capacitor C1 'and the inductor L1' is formed by the conduction of the diode D1. Therefore, this parallel resonance circuit becomes a resonance state and blocks the current flowing through the receiving coil 50.

As a result, the receiving coil 50 is disabled during transmission. In this case, the first capacitor C1 'is
Since the capacitance can be selected without being affected by the impedance required for the power feeding unit, it is possible to obtain a sufficiently large blocking impedance.

Since the receiving coil 50 is not operating in this state, the conduction resistance of the diodes D1 and D2 forming the switching element does not cause the loss of the receiving coil 50.

When the switching element is in a non-conducting state at the time of reception, the series connection circuit of the first capacitor to the third capacitor works as a tuning capacitor.
Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonant circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting the received signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding section can be maintained at an appropriate value. The second capacitor C2 'is short-circuited by the diodes D1 and D2. Therefore, in addition to the disconnection of the element by the parallel resonant circuit described above, the input of the reception amplifier 70 is short-circuited, and thus it is possible to prevent a large voltage induced during transmission from being applied to the reception system.

<Receiving> FIG. 9 shows an equivalent circuit in the receiving coil 50 shown in FIG. 7 when the diode D1 and the diode D2 are in the non-conducting state (during receiving operation) due to the reverse bias from the bias circuit 61. It is a circuit diagram.

In this case, the series circuit is composed of the first capacitor C1 'to the third capacitor C3 by the non-conduction of the diodes D1 and D2. Therefore, the combined capacitor of this series circuit becomes resonant with the inductor L0 at the Larmor frequency to perform the receiving operation. As a result, the receiving coil 50 becomes valid during reception.

Since the first capacitor C1 'and the second capacitor C2' are connected in series, the combined capacitance approaches the small value of the small first capacitor C1 'as described above.

Therefore, the second capacitor C2 'sets the impedance required for the power feeding portion to an appropriate value (for example,
It becomes possible to select a large capacitance for making it 50 Ω).

In this state, the receiving coil 50 is in the operating state, but the diodes D1 and D2 forming the switching element are in the non-conducting state, and the conduction resistance of the switching element does not cause a loss during reception. .

Further, in this case, since the switching element is in the non-conducting state and is not related to the current flowing through the MRI RF coil, the loss of the switching element does not affect the operation.

<Effects Obtained by the Embodiments> As described in detail above, according to the above-described embodiments, the following effects can be obtained.

If the combined capacitance of the capacitors connected in series has a value suitable for the tuning capacitor, the capacitances of the first capacitor C1 'and the second capacitor C2' can be freely selected.

Therefore, the first capacitor forming the parallel resonance circuit as the blocking circuit has a small value, and the second capacitor C2 'forming the power feeding section has an impedance suitable for outputting the reception signal. You can choose a large value.

With such a configuration, as described with reference to FIG. 4, it is possible to increase the blocking impedance and to keep the impedance of the power feeding portion at a low value. It becomes possible to achieve both.

When the receiving coil 50 is invalid, the diode D
Since 1 and D2 are in the conducting state and the diodes D1 and D2 are in the non-conducting state when the receiving coil 50 is valid, the diodes D1 and D2 are irrelevant to the current (reception signal) flowing through the MRI RF coil during reception. Therefore, the conduction resistances of the diodes D1 and D2 do not affect the operation of the receiving coil 50.

Therefore, for MRI which is provided with an effective / ineffective switching circuit capable of obtaining a sufficiently large blocking impedance without causing a problem such as loss at the time of switching, and also considering impedance matching with a receiving system. An RF coil can be realized.

Further, the MRI apparatus is provided with an effective / ineffective switching circuit capable of obtaining a sufficiently large blocking impedance without causing a problem such as loss upon switching, and in consideration of impedance matching with a receiving system. Can be realized.

With the provision of the third capacitor C3,
By keeping the capacities of the first capacitor to the third capacitor in a predetermined relationship, the potential with respect to GND can be minimized on the coil. Therefore, the current flowing through the stray capacitance to the subject can be minimized, and the loss of the coil and the heat generation of the subject can be minimized.

<Embodiment> By providing the third capacitor C3 and the inductor L3 'constituting a parallel resonance circuit in the above embodiment and providing D3 as the third switching means, the second parallel circuit is provided. It is also possible to configure a resonance circuit. This is shown in FIG.

The structure shown in FIG. 10 has an advantage that a larger blocking impedance can be obtained by the two parallel resonant circuits (L1'-C1 ', L3'-C3). When a reverse bias is applied to the switching element, the equivalent circuit is the same as that shown in FIG. 9 and the same operation as that of the embodiment is performed.

<Embodiment> In the above-mentioned embodiments and examples, the valid / invalid switching at the time of switching the transmission / reception in the receiving coil has been described, but it can also be used in the following. Is possible.

Valid / invalid switching when transmitting / receiving is switched in the transmitting coil: Valid / invalid switching when transmitting or receiving is performed in the transmitting / receiving coil: Similar operation is possible in the above two cases. It is possible to achieve both impedance matching and blocking impedance.

[0158]

According to the invention described in detail above, the following effects can be obtained. (1) In the MRI RF coil according to the first aspect of the invention, a tuning capacitor in which first and second capacitors are connected in series, and an inductor provided so as to form a parallel resonant circuit with the first capacitor are provided. In a conducting state, a parallel resonance circuit is configured by the first capacitor and the inductor, and in a non-conducting state, a switching means for connecting the first and second capacitors in series in an element, in the transmission / reception. An effective / ineffective switching circuit is provided in the element, and a signal is input or output from both ends of the second capacitor.

Therefore, when the switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance, so that the operation as the MRI RF coil is stopped. To do.

In this case, although the switching element is in the conducting state, the resonance circuit is in the parallel resonance state and the RF for MRI.
Block the current through the coil. Moreover, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding unit, it becomes possible to obtain a sufficiently large blocking impedance.

When the switching element is in a non-conducting state, the series connection circuit of the first capacitor and the second capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonant circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting the received signal. You can choose such a large value.

With this structure, the blocking impedance can be increased and the impedance of the power feeding portion can be maintained at an appropriate value. (2) In the MRI RF coil of the second invention, a tuning capacitor in which first and second capacitors are connected in series and a parallel resonant circuit with the first capacitor via the first switching means are configured. And a second switching means connected in series with the first switching means and arranged in parallel with the second capacitor.
An invalidation switching circuit is provided in the element, and a signal is input or output from both ends of the second capacitor.

For this reason, when the first switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance. The operation stops.

In this case, the first switching element is in the conducting state, but the resonance circuit is in the parallel resonance state and the MRI is performed.
The current flowing through the RF coil for use is blocked. Therefore, the first
The conduction resistance of the switching element is not a loss of the RF coil for MRI.

Further, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding section, it becomes possible to obtain a sufficiently large blocking impedance. Further, since the second switching elements on both ends of the second capacitor are in the conductive state, an unnecessary signal is not supplied or output.

When the switching element is in a non-conducting state, the series connection circuit of the first capacitor and the second capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonance circuit has a small value, and the second capacitor forming the power supply section has an impedance suitable for outputting a reception signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding section can be maintained at an appropriate value. (3) An MRI RF coil according to a third aspect of the invention is a connection between a tuning capacitor including a first capacitor and a second capacitor connected in series, the first capacitor and the second capacitor. A first switching means having one end connected to a point, one end connected to one end on the first capacitor side of the capacitor, the other end connected to the other end of the first switching means, An inductor that resonates in parallel with the first capacitor at a frequency, one end of which is connected to the other end of the tuning capacitor, and the other end of which is connected to a connection point between the first switching means and the inductor. A second switching means arranged so as to be turned on / off together with the switching means, and an effective / ineffective switching circuit at the time of transmission / reception. With, and configured to perform input or output of signals from both ends of the second capacitor.

Therefore, when the first switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance, so that the MRI RF coil is used. The operation stops.

In this case, the first switching element is in the conducting state, but the resonance circuit is in the parallel resonance state and the MRI is performed.
The current flowing through the RF coil for use is blocked. Therefore, the first
The conduction resistance of the switching element is not a loss of the RF coil for MRI.

Further, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding section, it becomes possible to obtain a sufficiently large blocking impedance. Further, since the second switching elements on both ends of the second capacitor are in the conductive state, an unnecessary signal is not supplied or output.

When the switching element is in the non-conducting state, the series connection circuit of the first capacitor and the second capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonant circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting the received signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding section can be maintained at an appropriate value. (4) In the MRI RF coil according to the fourth invention, a tuning capacitor in which first to third capacitors are connected in series, and an inductor provided so as to form a parallel resonant circuit with the first capacitor. In a conducting state, a parallel resonance circuit is formed by the first capacitor and the inductor, and in a non-conducting state, a switching means for connecting the first to third capacitors in series in the element. An effective / ineffective switching circuit is provided in the element, and the tuning capacitor is configured such that the combined capacitance of the first capacitor and the second capacitor is equal to the capacitance of the third capacitor. The signal is input or output from both ends of the capacitor.

For this reason, when the switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance, so that the operation as the MRI RF coil is stopped. To do.

In this case, although the switching element is in the conducting state, the resonance circuit is in the parallel resonance state and the RF for MRI.
Block the current through the coil. Moreover, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding unit, it becomes possible to obtain a sufficiently large blocking impedance.

When the switching element is in a non-conducting state, the series connection circuit of the first capacitor to the third capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonance circuit has a small value, and the second capacitor forming the power feeding section has an impedance suitable for outputting the reception signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding section can be maintained at an appropriate value. And
By providing the third capacitor C3 and maintaining the capacities of the first capacitor to the third capacitor in a predetermined relationship, it is possible to minimize the potential to GND on the coil,
The current flowing through the stray capacitance to the subject can be minimized, and the loss of the coil and the heat generation of the subject can be minimized.

It is also possible to provide an inductor forming a parallel resonance circuit with the above third capacitor and a switching element for operating this parallel resonance circuit, so that a larger blocking impedance can be realized. .

(5) In the MRI RF coil according to the fifth aspect of the invention, a tuning capacitor in which the first to third capacitors are connected in series and a parallel resonance circuit with the first capacitor are provided. And a switching means for forming a parallel resonant circuit with the first capacitor and the inductor in the conductive state and for connecting the first to third capacitors in series in the element in the non-conductive state. In the element, a valid / ineffective switching circuit is provided in the element, and the tuning capacitor is configured such that the combined capacitance of the second capacitor and the third capacitor is equal to the capacitance of the first capacitor,
A signal is input or output from both ends of the second capacitor.

Therefore, when the switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance, so that the operation as the MRI RF coil is stopped. To do.

In this case, although the switching element is in the conducting state, the resonance circuit is in the parallel resonance state and the RF for MRI is used.
Block the current through the coil. Moreover, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding unit, it becomes possible to obtain a sufficiently large blocking impedance.

When the switching element is in the non-conducting state, the series connection circuit of the first capacitor to the third capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonance circuit has a small value, and the second capacitor forming the power supply section has an impedance suitable for outputting a reception signal. You can choose such a large value.

With this structure, the blocking impedance can be increased and the impedance of the power feeding portion can be maintained at an appropriate value. And
By providing the third capacitor C3 and maintaining the capacities of the first capacitor to the third capacitor in a predetermined relationship, the GND potential on the coil can be minimized.
The current flowing through the stray capacitance to the subject can be minimized, and the loss of the coil and the heat generation of the subject can be minimized.

It is also possible to provide an inductor forming a parallel resonance circuit with the third capacitor and a switching element for operating this parallel resonance circuit, and it is possible to realize a larger blocking impedance. .

(6) MR shown in (1) to (5) above
Since the switching means in the RF coil for I is composed of a PIN diode, the high frequency impedance is high during reverse bias, the forward resistance is low during forward bias, and the resistance becomes pure resistance even at high frequencies. Is obtained.

(7) The MRI apparatus according to the present invention has an MRI RF coil equipped with an effective / ineffective switching circuit for switching effective / ineffective during transmission / reception in an element, and switching for switching the operation of the effective / ineffective switching circuit With a control circuit,
The effective / ineffective switching circuit forms a parallel resonance circuit with the tuning capacitor, in which a first capacitor for the parallel resonance circuit and a second capacitor for the power feeding unit are connected in series, and the first capacitor. A switching means for forming a parallel resonant circuit with the inductor provided and the first capacitor and the inductor in the conductive state, and connecting the first and second capacitors in series in the element in the non-conductive state; Configured.

Therefore, when the switching element is in the conducting state, the first capacitor and the inductor form a parallel resonant circuit, and the parallel resonant state results in high impedance, so that the operation as the MRI RF coil is stopped. To do.

In this case, the switching element is in the conducting state, but the resonance circuit is in the parallel resonance state, and the RF for MRI is used.
Block the current through the coil. Moreover, since the capacitance of the first capacitor can be selected without being affected by the impedance required for the power feeding unit, it becomes possible to obtain a sufficiently large blocking impedance.

When the switching element is in the non-conducting state, the series connection circuit of the first capacitor and the second capacitor works as a tuning capacitor. Therefore, if the combined capacitance has a value suitable for the tuning capacitor, each capacitance can be freely selected.

Therefore, of the capacitors connected in series, the first capacitor forming the parallel resonance circuit has a small value, and the second capacitor forming the power supply section has an impedance suitable for outputting the received signal. You can choose such a large value.

With this configuration, the blocking impedance can be increased and the impedance of the power feeding section can be maintained at an appropriate value.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a principle circuit configuration of a main part of an MRI RF coil and an MRI apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an equivalent circuit when the switching means is conducting in the principle circuit configuration of the MRI RF coil according to the embodiment of the present invention.

FIG. 3 is a configuration diagram showing an equivalent circuit when the switching means is non-conductive in the principle circuit configuration of the MRI RF coil according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram comparing the configuration of an MRI RF coil according to an embodiment of the present invention with a conventional MRI RF coil.

FIG. 5 is a configuration diagram showing a principle circuit configuration of a main part of the MRI RF coil and the MRI apparatus according to the embodiment of the present invention.

FIG. 6 is a configuration diagram showing an overall configuration of an MRI apparatus using an MRI RF coil provided with a blocking circuit.

FIG. 7 is an RF coil for MRI in which a blocking circuit includes three capacitors and an M coil according to an embodiment of the present invention.
It is a block diagram which shows the principle circuit structure of the principal part of RI apparatus.

FIG. 8 is a configuration diagram showing an equivalent circuit when switching means is turned on in the principle circuit configuration of an MRI RF coil having three capacitors in a blocking circuit as an embodiment of the present invention.

FIG. 9 is a configuration diagram showing an equivalent circuit when the switching means is non-conductive in the principle circuit configuration of the MRI RF coil having three capacitors in the blocking circuit as an embodiment of the present invention.

FIG. 10 is a configuration diagram showing a principle circuit configuration of a main part of an MRI RF coil and an MRI apparatus including three capacitors in a blocking circuit and two parallel resonance circuits as an embodiment of the present invention. .

FIG. 11: R for MRI equipped with a conventional blocking circuit
It is a block diagram which shows the principle circuit structure of an F coil.

FIG. 12: R for MRI equipped with a conventional blocking circuit
It is a block diagram which shows the principle circuit structure of an F coil.

FIG. 13 is a configuration diagram showing a principle circuit configuration of a conventional MRI RF coil provided with a C-division type blocking circuit.

[Explanation of symbols]

 50 receiver coil 61 bias circuit 62 blocking circuit 70 receiver amplifier C1 'first capacitor (for parallel resonance) C2' second capacitor C3 third capacitor L1 'inductor (for parallel resonance) L3' inductor (for parallel resonance) D1 diode (switching element) D2 diode (switching element) D3 diode (switching element)

Claims (7)

[Claims] 1. A tuning capacitor in which first and second capacitors are connected in series, an inductor provided so as to form a parallel resonant circuit with the first capacitor, and the first capacitor in a conductive state. And a parallel resonance circuit with the inductor, and a switching means for connecting the first and second capacitors in series in the element in a non-conducting state, and an effective / ineffective switching circuit for transmission / reception in the element. An RF coil for MRI, comprising: inputting or outputting a signal from both ends of the second capacitor. 2. A tuning capacitor in which first and second capacitors are connected in series, and an inductor provided so as to form a parallel resonant circuit with the first capacitor via a first switching means, A second switching means connected in series with the first switching means and arranged in parallel with the second capacitor; An MRI RF coil which inputs or outputs a signal from both ends of a second capacitor. 3. A first capacitor and a second capacitor connected in series
And a first switching means having one end connected to a connection point between the first capacitor and the second capacitor, and one end of the capacitor on the first capacitor side. An inductor which is connected to one end of the first switching means and the other end of which is connected to the other end of the first switching means and which resonates in parallel with the first capacitor at a frequency of a high frequency magnetic field; and one end of which is connected to the other end of the tuning capacitor. And the other end is connected to the connection point between the first switching means and the inductor, and the second switching means is arranged to be turned on / off together with the first switching means. And a signal input or output from both ends of the second capacitor. For MRI RF coil to the butterflies. 4. A tuning capacitor in which first to third capacitors are connected in series, an inductor provided so as to form a parallel resonant circuit with the first capacitor, and the first capacitor in a conductive state. And a parallel resonance circuit with the inductor, and a switching means for connecting the first to third capacitors in series in the element in a non-conducting state, and an effective / ineffective switching circuit for transmission / reception in the element. The tuning capacitor is configured such that the combined capacitance of the first capacitor and the second capacitor is equal to the capacitance of the third capacitor, and a signal is input from both ends of the second capacitor or An RF coil for MRI, which outputs. 5. A tuning capacitor in which first to third capacitors are connected in series, an inductor provided so as to form a parallel resonant circuit with the first capacitor, and the first capacitor in a conductive state. And a parallel resonance circuit with the inductor, and a switching means for connecting the first to third capacitors in series in the element in a non-conducting state, and an effective / ineffective switching circuit for transmission / reception in the element. The tuning capacitor is configured such that the combined capacitance of the second capacitor and the third capacitor is equal to the capacitance of the first capacitor, and a signal is input from both ends of the second capacitor. An RF coil for MRI, which outputs. 6. The RF coil for MRI according to claim 1, wherein the switching means is a PIN diode. 7. An RF for MRI equipped with an effective / ineffective switching circuit for switching effective / ineffective during transmission / reception in an element.
An MRI apparatus comprising: a coil; and a switching control circuit that switches the operation of the valid / invalid switching circuit, wherein the valid / invalid switching circuit includes a first capacitor for a parallel resonant circuit and a second capacitor for a power feeding unit. Tuning capacitor in which the above capacitors are connected in series, an inductor provided so as to form a parallel resonance circuit with the first capacitor, and a parallel resonance circuit including the first capacitor and the inductor in a conductive state. And a switching means for connecting the first and second capacitors in series in the element in the non-conducting state.